The previously sketched pacemaker is preferably an ICD (implantable cardioverter/defibrillator) with overdrive stimulation for the preventative treatment of atrial fibrillation. Customarily, such an ICD also has a connection for a ventricular electrode wire and a stimulation impulse generator for ventricular stimulation impulses that are effective in the ventricle of a heart.
In the case of the present invention, the problem of atrial fibrillation stands at the forefront. Atrial fibrillation affects a significant portion of the older population. One distinguishes two types of atrial fibrillation, namely, vagally-transmitted atrial fibrillation and adrinergic atrial fibrillation. The first-mentioned vagally-transmitted atrial fibrillation occurs in patients who are in a relaxed state, for example, during periods of digestion following meals or during the night or early morning hours. Preliminary results of clinical studies suggest that pacemakers or fibrillators that have a mode for preventative stimulation for the purpose of controlling atrial fibrillation are capable, at least by means of the so-called overdrive pacing, of at least reducing the length of vagally-induced atrial fibrillation episodes.
The overdrive stimulation known for limiting or preventing atrial fibrillation is based on the concept of permanently stimulating the largest possible number of atrial contractions and allowing the least number of natural (spontaneous intrinsic) contractions. For this reason, during overdrive stimulation, stimulation is accomplished either with a variable or a fixed, elevated atrial rate, for example, 80 to 90 beats per minute. In the case of the adaptive, variable overdrive stimulation, atrial stimulation occurs in such a way that the atrial stimulation interval corresponds to a length of approximately 95% of a corresponding natural (intrinsic) atrial interval. An example for such an adaptive overdrive algorithm is known as the applicant's DDD+ algorithm.
Since the generation of stimulation impulses requires a great deal of energy, overdrive stimulation leads to undesirably high power consumption. This impairs the life span of the pacemaker with overdrive stimulation.
The goal of the present invention is reducing the impairment to the life span of a pacemaker in conjunction with reducing or preventing atrial fibrillation.